Vehicles that travel at hypersonic speeds need an airframe designed to withstand thermal loads as well as structural loads. This is especially true for airframes designed with hot structure, whereby a portion of the vehicle structure is allowed to get hot, as opposed to a more traditional approach of using thermal protection materials on the vehicle surface. Structural configurations for wing-to-body joints that are typically used for aircraft are not appropriate for a vehicle with a hot structure wing. This is because the rigid connection of a traditional joint cannot accommodate the strain induced by thermal expansion, especially along the chord of the wing.
In most aerostructures, one or more primary load bearing members called spars create just a few paths to react to primary bending and shear loads. The spars may pass through the fuselage, under or over the fuselage, or connect directly to the fuselage. Regardless of position, a rigid connection is used to transfer wing loads into the fuselage. Typically, hypersonic vehicles are designed with parasitic thermal protection systems (TPS) on the skins of the vehicle that minimize internal structure temperature, thus enabling the traditional structural approach. TPS adds significant weight to the vehicle. It also adds cross sectional area to the vehicle and thickness to the wings in particular, which add significant drag forces at hypersonic speeds. A hot structure wing, whereby the wing is allowed to get hot from aerodynamic heating, would thus be much more efficient due to lower weight and reduced thickness. However, the thermal growth of the wing relative to the fuselage at extreme temperatures would overstress a traditional rigid connection, making it infeasible.
Thus, there is a need for a method of joining hot structure wings or control surfaces to the fuselage without overstressing the connection when relative thermal growth exists between structural members.